Some large gear drives are exposed to the environment and are not lubricated by circulating oil. Examples includes bull gears, girth gears, slew drive gears used for cranes, excavators, and other heavy equipment, gears used to rotate draw bridges, gears for ball mills, and also the final drive gear for steerable radar antennas on ships. Typically, a smaller pinion gear drives the large exposed gear.
Lubricating such gear drives with grease or another suitable lubricant is troublesome and messy. Sometimes, a brush is used to manually and periodically apply grease to the gear drive. Prior attempts at automatic grease applications resulted in waste and mess. When lubrication is ineffective, the result is wear of the gear drive. Moreover, even when the lubrication effort is effective, the result can be a waste of grease and/or grease contamination of adjacent equipment which, in the case of an antenna on board a ship, cannot be tolerated.